As a still image encoding scheme, JPEG is currently prevalent. JPEG was standardized by ISO (International Organization for Standardization). As a moving image encoding scheme, Motion JPEG that exploits JPEG as intra-frame coding is known. Furthermore, as the Internet proliferates, coding that can assure higher functions and higher image quality than JPEG used so far is demanded. For this reason, ISO is laying down new still image coding standards. This activity is generally called “JPEG2000”. Refer to Toda, “Special Report JPEG2000 Explore Next Generation Image Technique”, C MAGAZINE November 1999, pp. 6-10, for an outline of JPEG2000. A region ROI (Region of Interest) to be decoded to have higher image quality than surrounding portions is a new function, and is a helpful technique.
However, in a conventional image encoding/decoding apparatus (details will be described later), for example, when a communication line of a network having a low capacity is used, only a portion of the ROI is transported, and information other than the ROI is not transported at all. This is because the ROI has undergone a bit shift-up process to prevent bit planes from overlapping upon decoding inside and outside the ROI region, and if all bits of the ROI are not decoded, other bits cannot be decoded at all.
When JPEG2000 is applied as intra-frame coding to moving image coding, rate control is required, and the number of bit planes that can be transported may vary depending on patterns upon adjusting the code size. That is, the ROI and other regions can be reproduced in one frame, but only the ROI is reproduced and other regions are reproduced black in another frame. Furthermore, since different phenomena take place in units of frames, the reproduced image is disturbed considerably.
For example, upon encoding three successive frames, if the ROI and other regions can be encoded/decoded in an intermediate frame alone, as shown in FIGS. 18A to 18C, regions (background) other than the ROI in the frames shown in FIGS. 18A and 18C before and after the frame in FIG. 18B are not decoded, thus causing annoyance to the user.
The present invention has been made in consideration of the above problems, and has as its object to provide an image processing apparatus and method, that can satisfactorily encode and decode the ROI and other regions, and a computer readable memory.